Generally, it is well known to provide a subsurface well safety valve for use in a well for shutting off flow of well fluids through the well tubing. U.S. Pat. No. 4,161,219 issued July 17, 1979, discloses a piston actuated safety valve which is biased to an open position and is closed in response to hydraulic fluid applied from the well surface. In that valve the fluid pressure in the well conduit acts against the piston and cylinder assembly in a direction to move the valve to a closed position. However, in that case the pressure in the well conduit or tubing is working against the hydraulic control fluid from the surface which requires increased hydraulic control pressure acting against a tubing or conduit pressure which is undesirable, as well as variable, in some applications.
The present invention is directed to an improved piston and cylinder actuated subsurface safety valve in which the well pressure in the well conduit or tubing does not affect the opening or closing of the safety valve and thus provides a so-called balanced valve insofar as the effect of well tubing pressure is concerned.